The present invention relates to in electrical circuit and a system for producing such a circuit.
Conventionally, to mount a silicon device a circuit board is prepared. This generally consists of etched copper on glass fibre laminate, tin plated and possibly carrying further layers of lacquer for protection and labelling. Many operations of cropping, drilling, etching and plating are involved in its preparation. It is not cheap, and the production processes can have significant environmental impact.
The two major environment hazards posed by PCB manufacture are the waste effluent which is acidic and contains heavy metals, (especially copper) and the use of hydrocarbons in photoresist developer and stripper. Stricter pollution limits imposed by water authorities are one driving force to reduce copper in effluent. In theory, waste effluent could be eliminated by a totally additive process for copper deposition, which would also offer considerable cost savings, but a satisfactory process has not yet been developed.
Attempts to avoid the use of a circuit board as such include the use of both thick and thin film techniques, normally associated with higher cost, not lower. Resistors are formed on a ceramic substrate by depositing tracks of a suitable film, sometimes trimmed to precise values by laser etching. A film of higher conductivity is generally used for interconnection.
The present invention seeks to provide an improved electrical circuit and a system for producing such a circuit.
The research leading to this invention was directed towards techniques to print circuit board designs directly onto suitable substrates. One application of this technique is in substitutes for conventional (copper-clad resin/laminate) circuit boards where for low complexity circuits, directly printed substrates offer cost advantages and environmental benefits. The lithographic printing process sought to be used for this invention was considered to offer potential advantages in speed, hardware availability, and a small ink volume per unit, which would translate into additional financial and environmental benefits when compared to traditional screen printing and etched copper-clad laminate practice.
The use of lithographic processes for the manufacture of electronic and electrical circuit systems, including electrical interconnects and electrical and electronic components. The term xe2x80x9clithographic processxe2x80x9d referred to herein is a process for the printing of an electrically conductive film and passive components on a suitable substrate, utilizing differences in surface chemistry of the printing plate, including hydrophilic and hydrophobic properties. It does not refer to the commonly used process involving photoresist and etching occurring during the production of etched circuit boards and/or silicon semiconductor micro electronics. The term xe2x80x9cinkxe2x80x9d is intended to mean any material suitable for printing.
There are several important aspects of the developed lithographic circuit fabrication process, including:
A conductive ink
A lithographically printed circuit
Thus, according to an aspect of the present invention, there is provided an ink for the manufacture of an electrical circuit comprising electrically conductive particles suspended in a resin.
By ink it is intended to mean any liquid suitable for printing.
Preferably, the resin is an organic resin, such as an alkyd resin.
The conductive particles preferably consist of or include metallic silver. The metal content of the ink may be in-the range between 65% and 95% w/w, preferably between 650% and 90% w/w and most preferably about 80% w/w. The size of the metal particles may be in the range between 0.1 and 10 micrometres and preferably about 1 micrometre.
If aluminium or another conductive particulate is employed the w/w percentage will vary as the materials have differing densities, a metal coated particulate could be very light resulting in a low w/w percentage. A range of 15% or 20% w/w to 95% w/w is envisaged for these metals.
The ink preferably exhibits thixotropic flow properties of about 10.3 PaS @ 25xc2x0 C.
According to another aspect of the present invention, there is provided an electrical circuit board including a substrate, an electrical circuit lithographically printed onto the substrate from an ink as specified herein.
The circuit board may include one or more electrical components and a conductive component fixative binding the or at least one circuit component to the electrical circuit.
The component fixative preferably includes a metal-loaded or conductive adhesive as herein specified.
The substrate may be a paper such as gloss art paper, bond paper or a semi-synthetic (for example polyester fibre) or synthetic papers (for example Polyart), or plastics (for example Polyethylene), or composite materials (for example FR4 or FR2).